Chapter 6: Chapter Six: Fingerprint Identification

The police station courtyard was much quieter than usual.

In Ningtai County, a city of hundreds of thousands, serious crimes occur infrequently; over the course of a year, there might be ten or so unnatural deaths, and only one or two of those would become criminal cases—what are called homicides.

Precisely because of this, even though this case seemed straightforward, the Criminal Investigation Team deployed everyone.

Jiang Yuan returned to his office and found the fourth floor, where the Forensic Science Team worked, completely empty—only the Trace Evidence Office door was open, someone inside busily typing.

“Write the report in detail—this case might end in a death sentence, and the review standards for capital cases are extremely strict,” Wu Jun reminded Jiang Yuan, then added: “Back when we handled a case, one piece of evidence was a plastic oil drum. Two years after closing the case, we suddenly got a call asking why the photo showed a white drum when the actual evidence was yellow.”

Jiang Yuan turned on his computer while listening, curious: “Why?”

“Why? Because the plastic aged over time. We had to prepare supplemental materials. I’m telling you this to emphasize: death sentence reviews are far stricter than other cases—dozens of eyes are watching. Raising the standard won’t hurt.”

“Understood.” Jiang Yuan nodded obediently, then paused and asked: “What about my relationship with Uncle Seventeen… should I recuse myself?”

“Only close relatives need to.” Wu Jun’s definition of “close relative” varied across legal statutes—broadest in administrative law, narrowest in criminal law, limited only to spouses, parents, children, and full siblings.

Jiang Yuan relaxed and focused on his work.

Soon, a neat row of photographs appeared before him.

Uncle Seventeen’s intestines, Uncle Seventeen’s heart, Uncle Seventeen’s brain sections, Uncle Seventeen’s gastric contents… Jiang Yuan carefully selected and annotated each one.

For police officers, the complexity of case processing often far exceeds the actual solving of the case. Even in this seemingly simple murder, with the suspect confessing, the paperwork alone was endless.

Just before quitting time, noise erupted from the courtyard.

Jiang Yuan looked out the window and saw all three police cars parked inside; Liu, captain of the Second Squad, stood rigidly in front of the central vehicle, fully equipped as if facing a major threat.

Aunt Seventeen, thin and with a vacant stare, was led out from the back seat, handcuffed.

To be honest, Jiang Yuan had no strong memories of Aunt Seventeen. Before taking the civil service exam, he spent five years studying medicine elsewhere; before college, he attended boarding high school for three years. His impression of Aunt Seventeen was far weaker than his memory of Uncle Seventeen’s big belly…

“The suspect identified the murder weapon—a chef’s knife—thrown into a trash bin outside the residential compound,” Wu Jun also stood to watch below, updating Jiang Yuan on the case.

Jiang Yuan exhaled. The case had reached this stage—the investigation was essentially over, especially with the weapon discarded and the suspect pointing to a different location; the difficulty of overturning it was more than ten times greater than relying solely on testimony.

“What about the body disposal? She couldn’t have moved it alone.” Jiang Yuan asked another question.

“Her brother helped—used the store’s vegetable delivery tricycle and handcart,” Wu Jun paused, then added: “He’s been arrested and confessed.”

With both physical evidence and confession now complete, the case was essentially ironclad.

As Jiang Yuan drifted in thought, a semi-transparent system interface popped up.

Task: Conduct a full autopsy to assist in solving the case.

Reward: Chongqing Single-Fingerprint Analysis Method—Arch Pattern Identification (LV3).

Jiang Yuan stared, watching a silver dumpling fly into his forehead.

A flood of information surged chaotically into his mind.

The Chongqing Single-Fingerprint Analysis Method is one type of single-fingerprint analysis, among the earliest adopted domestically, designed specifically for cases with only one fingerprint—or even a partial, incomplete one. Similar methods include Qingdao’s single-fingerprint analysis domestically, and Bartlett’s classification method internationally. No method is inherently superior; they differ mainly in fingerprint classification and slight variations in analytical approach.

In short, it’s a technique for comparing fingerprints.

Jiang Yuan’s eyes brightened slightly—fingerprint comparison was the cornerstone of trace evidence work, and mastering it took years of grueling effort. To receive it directly from the system instantly boosted his sense of satisfaction.

Still, fingerprint comparison was no easy task.

Machines that could simply scan any fingerprint photo and instantly find matches simply didn’t exist.

Internationally mature fingerprint recognition systems (AFIS)—whether using RBNEC, American COGENT, or French Morpho—all relied on human annotation of fingerprint features—known as minutiae—then automatically matched and retrieved these points in the system, scoring candidates by similarity to generate a ranked list.

This was because fingerprints deformed under pressure, often nonlinearly; they frequently shifted or overlapped, poor preservation was common, and fingerprints found at crime scenes were often incomplete.

In short, automated fingerprint recognition required human preprocessing.

Devices like employee time clocks could only determine if two fingerprints were identical, and their accuracy fell far short of police requirements.

Wu Jun noticed Jiang Yuan’s distracted expression and cleared his throat twice: “Nothing much left. If you want to leave, go ahead—I’ll handle the rest.”

“Uh… really?” Jiang Yuan hesitated. He wanted to test his new skill, but trying it at home wouldn’t hurt either.

“We’ve got just this much work—finish it and we’re done.” Wu Jun lifted his chin proudly; compared to the officers below now scrambling to work, the forensic team’s duties were already over.